Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2018

Thesis Director

Robert E. Colombo

Thesis Committee Member

David H. Wahl

Thesis Committee Member

Scott J. Meiners

Abstract

Anthropogenic modifications, like impoundments, have altered natural environmental conditions in most lotic systems and impacted fish ecology in many ways. We examined the effect of large river impoundments on fish reproductive behavior by studying the larval fish communities in tributaries of the impounded Illinois and unimpounded Wabash Rivers. We hypothesized that larval fish communities would be similar between the geographically proximal systems, but temporal structuring would depend largely on flow regimes. Biweekly larval densities were greatest among all taxa in the Wabash system, though overall communities were similar between systems. Of the six tributaries, the four smallest rivers were most similar in assemblage structure, and the two largest tributaries were more diverse. All tributaries demonstrated larval community shifts from spring to summer, but Illinois River tributaries exhibited greater temporal variability. The large rivers had distinctive hydrographs, with differences in peak amplitude, duration, timing, and rate of water level change. Regulation of flow on the Illinois River was shown to mediate river fluctuations in its tributaries. Consequently, fish that depend on high water events for spawning in tributaries may not receive a strong cue in Illinois River tributaries and instead spawn in the Illinois River. Subsequently, larval production in large, impounded lotic systems may be concentrated in the larger rivers of these systems, and more evenly distributed among rivers in free-flowing systems.

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